Yeah, it didn't start then either. But I ran into Viola when I was looking to see if Susanna was still alive, and yep, they both are.
Well, I suggest you load up a save, before you have broken/entered in to Hjerim, and go an do other things for a while (complete few other quests) and then comeback & save and repeat the things you need to do to trigger the quest and see how it goes.
I often found that quest that didn't trigger, eventually did after completing few other quests in the journal.